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Knickerbocker Floodplain

  • Project area
  • Elements of the creek design
  • Floodplain design

The Knickerbocker floodplain site is a section of the South Branch of Thornton Creek in Northeast Seattle.  This project will relocate several hundred feet of the creek and create a 1.5 acre vegetated floodplain. This increased storage capacity will provide benefits to downstream stream-side properties and improve the habitat for biological communities within the creek. A new pedestrian bridge over the creek will be built as well.

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Project Updates

November 6, 2014

  • Woody debris at a turn in the creek
  • Plunge pool and carefully placed woody debris
  • Downstream view from the bridge
  • One of many monitoring tubes to help measure water quality and healthy microbes
  • Upstream view from the bridge
  • New plants around the pedestrian bridge

Construction of the Knickerbocker Floodplain Restoration project is now complete. We want all of our neighbors to know that we are truly grateful for your patience. This was a challenging project to complete on such a short schedule and in such a tight space. Check out this short video about the project.

Now that construction is finished, you’ll see a few remaining activities and materials.

  • Burlap ground cover and sandbags will remain as the plants become more established.
  • We have installed temporary fencing to discourage access to the newly planted floodplain and to protect the plants.
  • Workers will be onsite approximately monthly to inspect and care for plants. They will replace plants that are dead or dying due to natural causes, but not plants damaged by people. While it may be tempting to go exploring, we hope you and your pets stay on the path and the bridge so the new plants stay healthy.

October 22, 2014

  • Water Flowing in Thornton Creek

The project is nearly complete! Our contractor is finishing the landscaping and completing some minor repairs and cleanup as they get ready to leave the site. We expect the pedestrian bridge to be fully open -- not just during the school commute -- by this weekend.

You can contribute to the success of the project!
Thousands of new plants now cover the ground around the creek and they have an important role to play in the health of Thornton Creek. While it may be tempting to go exploring, we hope you and your pets stay on the path and the bridge so the new plants stay healthy.

October 3, 2014

  • Removing the dam
  • Thornton Creek flowing through the site

Thornton Creek is flowing once again! We removed the dam Tuesday and reopened the creek to water and fish.

Anticipated activities for the week of October 6:

  • Remove the creek bypass pipes from the site
  • Minor repairs to the bridge at the end of NE 100th St.
  • Work on the parking area
  • Landscaping

September 9, 2014

  • Pedestrial Bridge Open to StudentsThe pedestrian bridge is open for student use on weekday mornings and afternoons.

The pedestrian bridge is open! A handful of Sacajawea students and parents have been using the new pedestrian bridge since we opened it last Wednesday. This week we decided to open the bridge 15 minutes earlier in the afternoon to help parents get to the school in time to pick up their children.

New bridge hours
8:00 a.m. – 9:00 a.m.
2:30 p.m. – 3:30 p.m.

More bridge news
We’ve determined that the wooden bridge at the end of NE 100th Street will stay in place. Originally planned for removal, the bridge will continue to provide access to the north end of the area. We hope this is welcome news to the volunteers who help care for this natural area.

Anticipated activities for the week of September 8

  • Continued work on plunge pools and in-creek structures.
  • Excavate and shape the wetland area.

August 29, 2014

  • Installing the pedestrian bridge

We reached a major milestone this week when our contractor finished all of the in-creek work west of the new pedestrian bridge. This includes carving out the creek alignment, building log structures and drop pools for fish habitat and water quality, and laying the new creek bed.

The Seattle Department of Transportation also installed the new pedestrian bridge and expects to finish the final adjustments Tuesday. With an 85-foot span over the new creek, it will be ready to transport Sacajawea students when school starts next week. Please see the August 20 update on the project website for bridge opening hours and safety precautions.

Anticipated activities for the week of September 1:

  • Continue work east of the pedestrian bridge to build in-creek structures and shape the wetland and flood control areas.
  • Remove construction trailer.

August 20, 2014

  • Construction Drop Pools
  • Drop pools will contribute to water quality and fish habitat

Pedestrian Bridge Update
As part of Seattle Public Utilities’ Knickerbocker Floodplain Restoration project the Seattle Department of Transportation (SDOT) will replace the pedestrian bridge that crosses Thornton Creek on 20th Ave. NE between NE 100th St. and NE 98th St. SDOT plans to install the new bridge by September 3 to accommodate students who walk to Sacajawea Elementary, though weather or other unpredictable events could delay the opening.

Safety precautions
Seattle Public Utilities and our contractor will provide safety precautions for students during the school commute.

  • Fenced walkways on both ends of the bridge to keep students separate from construction work.
  • A flagger at each end of the bridge to alert crews when students are present and guide students safely through the pedestrian path.
  • Large equipment will pause when students are present.

The bridge will be open only during school commute times.

  • Morning: 8:00-9:00 a.m.
  • Afternoon: 2:45-3:30 p.m.

The bridge is scheduled to reopen to all pedestrians when construction is complete at the end of October.

Looking Ahead
While our past updates have focused on construction activities during the upcoming week, this week we want to give you a longer look at what you can expect between now and the end of the project.

We will continue to excavate and shape the new creek, including installation of log jams and drop pool structures that will make the new creek alignment function more naturally. SDOT expects to install the new pedestrian bridge during the end of August and have it open to students by September 3.

The Army Corps of Engineers extended the period of time when we are allowed to work in the creek from August 30th to September 30th. We will continue installing the log structures and drop pools, and then add the final streambed material.

The contractor will finish working outside of the creek. Work will include creating and enhancing the wetland around the creek and installing native plants in the new floodplain. Once this work is done, the contractor will remove fencing and equipment.

August 4, 2014

The site is dry again and the creek and floodplain are taking shape. We’ve begun to construct drop pools and log structures which are essential to the function of the new creek. Instead of allowing the water to flow quickly through the area in a narrow channel, the drop pools will slow the creek, create quiet spaces, and improve water quality. The first drop pool is nearly complete with five more to build.

In response to community concerns, we are installing scrubbers on the diesel generators to reduce exhaust fume odors and relocating the generators and pumps further from homes to reduce noise. We would like to thank all of our neighbors for your ongoing patience. We understand that construction is a disruption to your daily lives. If you have specific concerns, please don’t hesitate to contact us.

Other upcoming construction activities:

  • Constructing the pedestrian bridge footings
  • Placing large rocks
  • Saturday work will continue in order to complete in-water work within the fish window period. Crews can begin work as early as 9:00 am.

July 18, 2014

  • Dry creek bed. The creek now flows through pipes around the project area.
  • A film crew is documenting our work on Knickerbocker and the Thornton Creek Confluence projects.

Our project is in full swing now. We continue to move a lot of soil to create the new creak alignment and build the vegetated floodplain. We have a challenging schedule and a lot of work to do.

Anticipated work during the upcoming week:

  • Beginning this weekend, the contractor will work on some Saturdays. They plan to work between the permitted hours of 9 a.m. and 7 p.m. Weekend work will help us meet the “fish window” goal of completing the in-creek work in August.
  • Continued excavation of the creek and floodplain. Trucks will haul material away from the site.
  • Drilling and pumping groundwater out of the excavation area. The contractor plans to use the excess water to control the dust onsite.

We realize construction activities can be inconvenient at times. Thank you for staying informed and for sharing your comments and concerns. Your opinions and feedback are very important to us!

July 11, 2014

It’s been a milestone week for the project. Specialists relocated about 400 fish from the project area, tagging and moving them to another section of the creek. The creek is now fully diverted with a dam at the top of the project area and pumps moving the water past the project area and back into the creek. This will allow the contractor to begin the work of recreating the creek and floodplain.

Nearby residents may also have noticed that SDOT delivered and removed a very large excavator this week. We understand that the early delivery impacted the neighborhood. Because of the excavator’s size and the technical challenges involved in bringing it to the project site, SDOT was only permitted to deliver it in the early morning hours, before traffic picked up. This was an isolated event in the project and we plan to maintain our 7 a.m. start time in the future.

Anticipated work during the week of July 14:

  • Major excavation of the creek and floodplain. Trucks will haul material away from the site.
  • Relocation of existing utility pipes in the project area.
  • Drilling and pumping groundwater out of the excavation area. The contractor plans to use the excess water to control the dust onsite.

June 19, 2014

Last week we held our final pre-construction meeting and gave the contractor, Magnus Pacific Corporation, formal permission to begin work. The contractor has begun to move equipment into the area and will continue to construct fencing to mark the construction area. Today they will begin to clear brush and trees from parts of the project area. They will also deliver an office trailer that will serve as the construction office during the project. Major work will begin the first week of July.

Please remember this is now an active construction site. Access to the site will be closed by Monday, June 23rd. There will be no pedestrian access through the site throughout the summer and no access to the stairwells leading up to NE 98th St. Please keep away from equipment and leave signs and marking stakes in place.

During construction you can expect:

  • Construction noise and dust.
  • Access to neighborhood streets.
  • Truck traffic may cause periodic delays for homeowners on NE 100th St., west of 21st Ave NE. A flagger will assist with local access during construction hours.
  • Regular garbage, recycling, and yard waste pickup.
  • Normal access to the west side of the creek during some of the construction.

May 15, 2014 Update

Construction will begin soon! We have awarded the contract to Magnus Pacific Corporation. We expect them to begin working in or around June and complete all the construction activities in October. Work in the creek will take place between July 1st and August 31st in an effort to protect fish populations. Normal work hours will be from 7 a.m. to 5 p.m., Monday through Friday.

You are invited to join the project team at a drop-in information session to discuss the project and the construction impacts on your neighborhood. The meeting will take place outdoors at the project site with members of the project team available to answer your questions.

Thursday, May 29
5:30 – 7:00 p.m.
NE 100th St. and 20th Ave. NE
(At the project site)

Update on the north-end element: While we made every attempt to fit the north-end part of the project (north of NE 100th Street) into our budget, the contractor bids we received were too high to include this work. We made the difficult decision to move forward with the project without the north-end element.

March 28, 2014 Update

The Knickerbocker project is in the advertisement phase and currently soliciting bids from prospective general contractors. SPU is requiring contractors to submit their bids no later than 2:00 p.m. on Wednesday, April 2, 2014. SPU has made a decision to include the north-end portion (north of NE 100th Street) of the project, as “additive work.” This decision was made strictly because of financial challenges to the project. It is SPU’s hope that the bids will come in lower than the engineer’s estimate. We are continuing to evaluate our options for retaining the north-end construction in the scope of work.

January 30, 2014 Update

A great deal of work has been going on to prepare for work at the Knickerbocker Floodplain site:

  • All permits have been obtained
  • Currently going through the City’s Department Circulation process to get signatures from other City Agencies (Seattle City Light, Seattle Dept. of Transportation, Parks)
  • Project Manual is being finalized in preparation for the upcoming Public Works process (ad, bid, award contract)
  • Finalizing the Memorandum Of Agreement (MOA) with Sound Transit
  • Contractor expected to be under contract with SPU by early May
  • Construction tentatively scheduled to start in early June (riparian, upland areas) and creek work will be done during the fish window (July1-Aug 30)
  • Two rounds of invasive removal was done last October and December; another round of noxious weed removal scheduled for next month (February)
  • Volunteer planting may be permitted after all construction activities have been completed, preferably in the Fall, and all work need to be coordinated with both SPU and Parks
  • The old pedestrian bridge will be removed and replaced with a new, longer pedestrian bridge

August 14, 2013 Update

Removal of invasive plant species is scheduled for August 28-30. The Seattle-based non-profit group EarthCorps will be performing this work. It will include both physical removal and treatment with an “eco-friendly” herbicide application, which will be reapplied in the spring. They will be targeting Japanese knotweed, nightshade and morning glory, English ivy, bamboo, blackberries and a variety of other non-natives.

Project Schedule

July 2014: Construction began.

September 30, 2014: End of the fish window, the period during which we are permitted to work within the creek. All in-creek work should be complete, including drop pools and log structures.

October 2014: Final out-of-creek work, including planting and landscaping.

Contact Us

For additional information, contact Arnel Valmonte, SPU Project Manager, at (206) 615-1438 or

Related Links

Lake Washington Watershed
Thornton Creek Alliance